This is the first reported study on Staphylococcus aureus carriage rate among patients with CKD compared to controls from Sri Lanka. Our key findings include high rates of S. aureus carriage among patients on haemodialysis and among patients who had received antibiotics recently. There was no methicillin resistance detected in our cohort and there was a good correlation between skin and nasal carriage.
Increased carriage among patients on haemodialysis noted in our study is comparable to reports from other countries (5). Hemodialysis patients are known to have poorer cell mediated immunity, antibody formation and phagocytic function and it has been suggested that such factors may increase the rates of colonization in this group. It would be interesting to observe the rates of colonization in patients with a similar degree of renal function who are on conservative management. In our cohort the median eGFR of the CKD 5 group was 13 ml/min and this would have been much higher than any residual renal function measured in the dialysis group. It is interesting that the rate of carriage in renal transplant patients with preserved graft function was 14.7% and was similar to that of controls. Most of our renal transplant recipients are on triple immunosuppression with prednisolone, a calcineurin inhibitor and an antiproliferative agent (azathiproine or mycophenolate mofetil) and the presence of good kidney function suggests that reasonable level of in-vivo immunsoppression had been achieved. This therefore indicates that there are factors beyond these arms of immunity that play a role in the high level of S. aureus carriage in the haemodialysis cohort. One explanation for the high rates of S. carriage in the haemodiaylsis cohorts is frequent exposure to health care settings and where cross contamination can occur with health care workers, and other patients. Further factors may be frequent venepuncture and the presence of prosthetic material. (10)
The concern regarding colonization in this population is the high risk of infection, particularly blood stream infection which has a high mortality. Up to 80% of the serotypes of Staphyloccocus causing blood stream infections are identical to isolates form the anterior nares and this suggests that most infection are auto-infections (1). We have no data on vascular access related infection rates in Sri Lanka, and this is an important area for research. Many of our patients present with advanced kidney disease, and are commenced on dialysis via temporary non-cuffed dialysis catheters that are kept in-situ for longer than advised by international recommendations. This is due to delays in access to theatre and radiological expertise for insertion of cuffed tunneled dialysis catheters and for creation of arteriovenous fistulae (AVF) or grafts (AVG). Therefore the bridging period between the initiation of haemodialysis and creation of an AVF is a high risk period for our patients. Our data was collected from patients who are already on haemodialysis and likely overestimates the prevalence of colonization in patients being initiated on haemodialysis. It would be interesting to prospectively follow up patients from the time of initiation of haemodialysis onwards, for colonization and infection rates within our cohort. Very few of our patients go on to receive long-term chronic dialysis, due to resource limitations, and therefore infection and colonization rates will be expected to differ from those from other settings. Eradication of S. aureus nasal colonization with topical mupriocin is known to reduce rates of Staphylococcus infection in haemodialysis patients (10). Information about our own infection rates will be useful for us to decide on the utility and cost-effectiveness of this approach in our setting.
Another interesting association we recognized was between antibiotic use during the preceding one month and Staphylococcus coonization. However, as this was a cross sectional study we could not conclude whether the skin carriage was the cause of more serious infection, subsequent to it or simply an association. There was no association between skin carriage and diabetes mellitus or recent hospitalizations in our study group (5). However there was a high rate of diabetes within our control group (54%) and all the MSSA positive patients from the control group were diabetic.
None of our patients had MRSA colonization. This is in contrast to some of the cohorts showing high rates of colonization by both methicillin sensitive and resistant Staphylococcus aureus (8). Further studies are required to determine whether this depicts lower rates of antibiotic resistance in our setting or whether it is a result of selection bias from a single outpatient unit.
We noticed very good correlation between skin and nasal carriage in our samples. Only one had skin carriage without nasal carriage. This highlights the possible utility of testing for skin carriage or nasal carriage alone to detect a possible carrier status. Prior studies have confirmed this and shown that nasal swabbing alone is adequate (8, 9). This is in keeping with the results from our study. A few studies have higher detection rates using throat swabbing (8, 9). We did not adopt this due to inconvenience to the patient. It is also possible that we may have detected more carriage had we repeated screening as for intermittent carriage.